There is a need for higher density magnetic recording and magnetic recording media meeting such a need are desired to be higher in coercive force and saturated magnetization.
Therefore, in magnetic recording media as typified by 8-mm video tape and DAT, metal magnetic powders based on iron having a high coercive force and high saturated magnetization are suitable and have been commercially used in magnetic layers.
Also, metal magnetic powders having a metal compound clad on the surface are known to have higher coercive force and high saturated magnetization.
Japanese Patent Application Kokai No. 60506/1983, for example, discloses a metal magnetic powder having at least one of the hydroxides of Cu, Ag, Al, Ti, Zr, Sn, V, Nb, Ta, Sb, Cr, Mo, W, and Ni applied to the surface. This powder uses an oxide magnetic powder such as .gamma.-Fe.sub.2 O.sub.3 as the core material.
In turn, Japanese Patent Application Kokai No. 159904/1984 describes a metal magnetic powder having a Zr compound applied thereto.
Also, Japanese Patent Application Kokai No. 162205/1984 discloses a metal magnetic powder having a Zr compound and an Si compound applied thereto.
Further, Japanese Patent Application Kokai No. 57701/1989 describes a metal magnetic powder having a Zr compound, an Al compound, and an Ni compound and/or a Cu compound applied thereto.
All these powders are prepared by adding an aqueous solution of a compound to a slurry of starting material particles of .gamma.-Fe.sub.2 O.sub.3 and .alpha.-FeOOH, thereby causing the compound to adhere to the starting material particles, and thereafter, effecting reductive reaction into metal magnetic powder. When it is desired to apply a plurality of compounds in a composite manner, aqueous solutions of respective compounds are prepared and applied separately.
Further, Japanese Patent Application Kokai No. 156209/1987 discloses to prepare a metal magnetic powder by applying a Zr compound to iron oxyhydroxide or iron oxide, and then applying at least one of an Si compound, a P compound, an Al compound and a B compound, followed by reduction.
Also, Japanese Patent Application Kokai No. 306526/1988 discloses a metal magnetic powder having at least one of an Al organic compound, a Ti organic compound, a Zr organic compound, and an Si organic compound applied to a metal magnetic powder and/or iron nitride magnetic powder.
Also, Japanese Patent Application Kokai No. 57701/1989 discloses a metal magnetic powder prepared by applying a Zr compound, an Al compound, and an Ni compound and/or a Cu compound to hydrous iron oxide or iron oxide and effecting reduction.
Furthermore, Japanese Patent Application No. 84076/1988 discloses to prepare a metal magnetic powder by applying a Co compound or Co ion to hydrous iron oxide and effecting reduction.
As to the 8-mm video tape technology, for example, a high-band 8-mm video version has been developed where higher output is required as well as further improvements in S/N and C/N.
In addition, for ensuring stable travel of media, it is required for the media to have a sufficiently low coefficient of friction .mu., typically of 0.35 or less.
Higher dynamic durability is also necessary.
However, magnetic recording media using metal magnetic powder as disclosed in the above-referred patent publications are difficult to achieve satisfactory surface smoothness, a low coefficient of friction .mu. during operation, and stable dynamic durability.
A significant loss of dynamic durability occurs particularly at low temperatures or at high temperatures and high humidity.
Electromagnetic properties including output, S/N and C/N are also unsatisfactory.